The present invention relates to a system for diagnosing trouble of an exhaust gas recirculation system for an automotive engine.
If trouble or malfunction occurs in the exhaust gas recirculation (hereinafter called EGR) system, the amount of NOx in the exhaust gases increases. Accordingly, a diagnosing system is provided for the EGR system so as to provide an alarm of the trouble or malfunction of the EGR system.
The troubles of the EGR system are for example sticking of a valve body of the EGR valve to a seat and tearing of a diaphragm. Therefore, for diagnosing the EGR system, it is necessary to accurately detect the operation of the EGR valve, and further, desirable to employ a detecting means having longer durability.
Japanese Patent Laid Open No. 55-123345 discloses a diagnosing system for the EGR system which produces an alarm when the opening degree of an EGR valve detected by a potentiometer deviates from a desired value over a predetermined allowable range.
The potentiometer has a sliding contact engaging with a resistance element, for detecting the EGR valve opening degree. However the contacts are subject to fail to produce a proper signal due to deterioration of the contacts, for example rust caused by salt included in the atmosphere.